Telephone companies have recently begun offering customers the option of having multiple ringing cadence capability on a single telephone line. In accordance with this capability, one or more additional telephone numbers, each of which has its own distinctive cadence, is added to the regular service on the installed line. A typical residential application would be to serve the needs of a household with teenagers, each of whom can be provided with a separate telephone having his or her own telephone number without the expense of a dedicated line. Instead, listening to the ringing tone allows members of the household to know for whom the call is intended, so that a particular individual can answer the call.
It goes without saying that such a service may also be utilized with devices other than personal telephones and in other than residential environments. For example, with the proliferation of different types of telephone line-connected communication equipment, such as facsimile communication devices and computer terminals, this multiple ringing cadence service offers the customer a mechanism of gaining more effective use of the telephone network without the costly burden of adding an additional line for each device. A major problem in utilizing the service is the fact that even though different devices may have been assigned respectively different numbers, every device will ring whenever any of the ringing cadences is present on the line, as every device is connected to the line. In the service option provided by the telephone company, selective answering of the call requires human intervention to know which device to pick up.
One proposal to solve this problem is described in the U.S. Pat. No. 4, 782,518, to Mattley et al, entitled "Apparatus for Converting Distinctive Ring to Selective Ring in Telephone Lines", issued Nov. 1, 1988. According to this patented scheme, the telephone line is coupled to the input port of a ringing cadence responsive multiplexer, multiple output ports of which are coupled to line devices having respectively different telephone numbers (associated with respectively different ringing cadences of the multi-ring service offered by the telephone company). Depending upon the ringing cadence of an incoming call, the input port is switched though one of plural sets of relay contacts of the multiplexer to one of its output ports, so that the associated line device may receive ringing signals. A basic shortcoming of this device is the fact that all subscriber line devices making use of the special service must be either located immediately adjacent to the device, or be routed to one of its output ports, usually by way of a dedicated length of cable through one or more rooms of a building between the subscriber device and the switch. Moreover, the Mattley et al device provides no indicator light or display to indicate which line is in use.